Don't mix up the idea of plural nouns - which relate only to countable nouns - and uncountable nouns. "book" is countable and so you can have three books (you can count them). "advice" is uncountable and like all uncountable nouns is always singular e.g. Love is in the air. Water tastes good. We need a "word + of" to indicate a unit of an uncountable thing e.g. a bottle of water, a block of cheese, a piece of advice. The uncountable noun stays in the singular (e.g. "three pieces of advice", not "three pieces of advices").

Think of advice as a more general term.. He gave me advice (we talked for a while and he told me a few things that helped me) A piece of advice is literally ONE suggestion.. He gave me a piece of advice (he told me one thing that helped me e.g. Always try to be nice.)

Hello Elena, The word advice is indeed uncountable, so you would never say something like "He gave me advices." In addition I would say "He gave me some advice" instead of "he gave me advice."

As far as I know that the word advice can't be made plural